A thermal storage system and temperature controlled container comprising the same

ABSTRACT

Passive thermal storage systems and methods comprising at least one thermal storage module for storing thermal energy in a predetermined temperature range, are disclosed. The thermal storage module comprises an FT unit and a Heat Storage (HS) unit at least partially filled with a first Phase Change Material (PCM). The HS unit comprises a container. The thermal storage module may be in the form of a stacked structure comprising the FT unit having a first wall with a first heat exchange surface and the HS unit having a second wall with a second heat exchange surface, the first and second heat exchange surfaces being in thermal contact with each other. The thermal storage system may be used to maintain the temperature of the payload of a temperature controlled container at a predetermined value or within a predetermined range.

TECHNICAL FIELD

The present invention relates to a thermal storage system arranged forstoring thermal energy, which is for example suitable for maintaining apayload space at a predetermined temperature. The present inventionfurther relates to a temperature controlled container comprising athermal storage system according to the present invention.

BACKGROUND ART

Phase change materials (PCM) are substances that absorb and releasethermal energy during the phase change. When a PCM freezes, it releasesa large amount of energy in the form of latent heat at a relativelyconstant temperature. Conversely, when such material melts, it absorbs alarge amount of heat for instance from the environment. As thermalenergy carrier, PCMs are ideal for a variety of everyday applicationsthat require temperature control. The most commonly used PCM iswater/ice. Ice is an excellent PCM for maintaining temperatures at 0° C.But water's freezing point is fixed at about 0° C. (32° F.), which makesit unsuitable for thermal energy storage applications at othertemperature levels. To address that limitation, PCMs have been developedfor use across a broad range of temperatures, from −40° C. to more than150° C. In contrast to water, many PCMs do not change phase at a singletemperature but they change phase over a temperature range of somedegrees Celsius. For instance a PCM with a peak phase change temperatureof −21° C. may already start freezing at −14° C. and is completelyfrozen at −26° C. The phase change temperature, which is commonlyreported on the data sheet of the PCM, is the peak temperature at whichthe highest amount of latent heat is released or absorbed. PCMstypically store 5 to 14 times more heat per unit volume than materialssuch as water, masonry or rock. Among various heat storage options, PCMsare particularly attractive because they offer high-density energystorage and store heat within a narrow temperature range.

PCMs have been used for the development of thermal storage systems,which can be used for maintaining a payload space at a predeterminedtemperature or in a predetermined temperature range for an extendedperiod of time, without the need for using an external power supply. Forexample, such thermal storage systems have been used in the developmentof passive refrigerator units used for transporting temperaturesensitive products that need to be maintained at a predeterminedtemperature for an extended period of time without the need ofconnection to an external power supply. WO2014178015 discloses anapparatus for preserving refrigerated or frozen products, particularlyfor thermally insulated compartments of refrigeration vehicles,refrigeration chambers or the like. The apparatus of WO2014178015 isprovided with heat accumulation elements filled with a heat accumulationliquid, which is a PCM material. Each of the heat accumulation elementsare provided with a heat exchanger element that can be supplied with aheat exchange fluid and that is submerged in the PCM. According toWO2014178015, the heat exchange element is immersed in the heataccumulation fluid. The heat exchanger element is arranged for chargingand discharging the heat accumulation element by pumping through theheat exchanger element a heat exchange fluid. More specifically, theheat exchange fluid is a single phase refrigerant in the form of aliquid or gas arranged to be pumped in and out of the heat exchangeelement by means of an external system until the heat accumulation fluidis charged or discharged. Once the charging or discharging process iscompleted, the passive refrigerator unit is disconnected from theexternal system and the heat transfer fluid is removed from the heatexchanger elements.

DE102013221918A1, EP1236960A1, DE19907250A1 and U.S. Pat. No. 6,094,933Adescribe temperature controlled containers that include a thermalstorage system with PCM material. The thermal storage system however iscoupled with an active thermal system requiring an external powersupply. The thermal system comprises a heat pump, employing thewell-known refrigeration-type cycle, while in use moving thermal energyin the opposite direction of spontaneous heat flow and in order toperform that work it requires an external power supply, the thermalstorage system allowing to change the performance of the thermal system.

DISCLOSURE OF THE INVENTION

It is an aim of the present invention to provide a thermal storagesystem, which is suitable for storing thermal energy at a predeterminedtemperature or temperature range and which can be used for example tomaintain a payload space of a temperature controlled container at apredetermined temperature or temperature range for a certain period oftime.

According to the present invention the term “charging” of the PCMmaterial refers to the process of storing thermal energy in the form of“heat” or “cold” in the PCM material.

According to the present invention the term “discharging” of the PCMmaterial refers to the process of thermal energy being released from thePCM material.

According to the invention the term “phase change temperature” of thePCM refers to the phase change temperature, which is for examplecommonly reported on the data sheet of the PCM, which is the peaktemperature at which the highest amount of latent heat is released orabsorbed. In case there is no temperature range at which the phasechange occurs but only a single phase change temperature, such as forexample with water when going from liquid to solid at 0° C., the singlephase change temperature corresponds to the peak temperature.

This aim is achieved according to the invention with the thermal storagesystem showing the technical characteristics of the characterising partof the first claim.

According to a first aspect of the present invention a thermal storagesystem is provided, which is suitable for storing thermal energy at apredetermined temperature or temperature range. The thermal storagesystem is provided with at least one thermal storage module, whichcomprises at least one Fluid Transporting (FT) unit and at least oneHeat Storage (HS) unit filled with a first Phase Change Material (PCM).The FT unit may be provided with a wall having a heat exchange surface.The at least one FT unit is provided with at least one passagewayarranged for receiving a heat transfer fluid, at least one inlet portfor the inflow of the heat transfer fluid to the passageway and at leastone outlet port for the outflow of the heat transfer fluid from thepassageway. The inlet and outlet ports of the at least one fluidtransporting unit are arranged for being releasably connected to a heattransfer fluid system, such as a chiller or a boiler, which heattransfer fluid system is arranged for supplying or releasing the heattransfer fluid from the at least one fluid transporting unit passagewayvia the inlet and outlet ports. The at least one HS unit is filled witha first Phase Change Material (PCM), the first PCM being arranged forexchanging thermal energy by at least partially changing from a firstphase to a second phase. The first PCM of the HS unit is arranged forbeing in thermal contact with the heat transfer fluid of the at leastone FT unit such that thermal energy can be transferred between the atleast one FT unit and the at least one HS unit so that the first PCM ofthe HS unit can change from the first to the second phase at a firstpredetermined phase change temperature.

According to embodiments of the present invention the at least one FTunit comprises the heat transfer fluid, the heat transfer fluid having apredetermined inlet temperature such that there is a non-zerotemperature difference between the inlet temperature of the heattransfer fluid in the FT unit and the phase change temperature of thefirst PCM in the HS unit allowing heat transfer between the heattransfer fluid and first PCM. The heat transfer fluid may be a pumpablesingle phase fluid or a pumpable multi phase fluid of which at least onesubstance changes phase during heat transfer. Examples of such apumpable multi phase fluid of which at least one component changes phaseduring heat transfer is a solid/liquid slurry or a vapour/liquidrefrigerant. A solid/liquid slurry, for instance an ice slurry or a PCMslurry, is preferred due to the lower pressures compared toliquid/vapour fluids. When disconnecting the at least one FT unit fromthe heat transfer fluid system, the heat transfer fluid can be removedfrom the FT unit or the heat transfer fluid can at least partiallyremain in the passageway of the at least one FT unit.

It has been found that by providing the at least one FT unit with a heattransfer fluid, which is maintained in the passageway of the at leastone FT unit upon disconnection of the heat transfer fluid system, alarger thermal energy density is obtained compared to the systems of theprior art. The thermal energy density is the amount of thermal energystored in the thermal storage system per unit of volume of the thermalstorage system. In the case where the heat transfer fluid is a multiphase fluid of which at least one substance changes phase during heattransfer the thermal energy density may be significantly higher due tothe latent contribution during phase change of the heat transfer fluid,which is not available when using a single phase heat transfer fluidwhich only has a sensible heat contribution. Moreover, the heat transfercoefficient of a multi phase fluid of which at least one substancechanges phase during heat transfer may also be significantly higher thanthe heat transfer coefficient of a single phase fluid. This maysignificantly increase the faster transfer of thermal energy between thefirst FT and HS unit, even when for example the heat transfer fluid isnot maintained in the passageway of the at least one FT unit upondisconnection of the heat transfer fluid system.

According to embodiments of the present invention, the FT unit may beprovided with a first wall having a first heat exchange surface and theHS unit may be provided with a second wall having a second heat exchangesurface, the first and second heat exchange surfaces being in thermalcontact with each other. For example, the thermal storage system may bein the form of a stacked structure, wherein the first and second wallsof respectively the FT and HS unit are in thermal contact with eachother. In this way, thermal energy can be exchanged between the firstPCM of the HS unit and the heat transfer fluid of the FT unit. Accordingto embodiments of the present invention, the first and second heatexchange surfaces of respectively the FT and HS unit may be in thermalcontact with one another via a common wall. According to embodiments ofthe present invention the HS unit may be a closed volume container atleast partially filled with the first PCM. For example, the HS unit maybe a container with at least one opening to fill the container with PCM.After at least partially filling the container with PCM the at least onefilling opening is sealed resulting in a closed volume container.Furthermore, the first and second heat exchange surfaces may be on anouter side of respectively the first and second walls of the FT and HSunit. For example, the HS unit and the FT unit may be placed on top ofone another such that their respective outer heat exchanging surfacesare in thermal contact. Such a configuration has been found to allow aneasier assembly of the different units into the module. Moreover, theuse of a common wall allows improving the thermal contact between the HSunit and the FT unit.

According to embodiments of the present invention, the thermal storagemodule may be in the form of a stacked structure comprising at least twoHS units, each being in thermal contact with the a respective heatexchange surface of the FT unit. The two HS units may contain adifferent PCM having a different phase change temperature.

According to embodiments of the present invention, the stacked structuremay be provided with a plurality of alternating layers of the HS unitand the FT unit. Different HS units may contain different PCMs. Byproviding a stacked structure with alternating layers of HS units andthe FT units the thermal energy that can be stored in the thermalstorage system may significantly increase. By keeping the HS units thin,the PCM in each HS unit can rapidly be at least partially charged ordischarged. The PCM charging or discharging process can further beaccelerated by adding heat conducting elements to the HS unit. If atleast two FT units are present in the thermal energy system their inletand outlet ports are connected to each other realizing a certain flowpath.

According to embodiments of the present invention, the HS unit and/orthe FT unit may in the form of a beam like structure, such as a panel,having a predetermined shape. For example, the FT unit and/or the HSunit may be in the form of a beam like panel having a rectangular shape.

According to embodiments of the present invention the HS unit and/or theFT unit may be provided with at least one undulated heat exchangesurface e.g. an outer heat exchange surface. The undulations mayincrease the available heat transfer surface and further increase themechanical strength of the thermal storage module.

According to embodiments of the present invention the PCM in the HSpanel may have a thickness of less than 40 mm, measured from the heatexchange surface in contact with the FT unit. For example, the HS panelmay have a thickness between 1 mm and 40 mm, preferably 5 mm and 20 mm.This limited thickness of the PCM ensures a fast charging or dischargingand further reduces the overall size of the thermal storage unit.

According to embodiments of the present invention, the at least one FTunit comprises an extruded profile comprising at least one passagewayfor the heat transfer fluid. In this way, the heat transfer fluid canefficiently be circulated in the at least one FT unit so as to reducethe time required for charging the first PCM material. The FT unit maybe provided with a plurality of passageways, thereby defining aplurality of flow paths for the heat transfer fluid.

According to embodiments of the present invention, the thermal storagemodule comprises an extruded profile comprising the at least onepassageway for the heat transferring fluid in the at least one FT unitand at least part of the at least one HS unit. Such an extruded profileprovides a high mechanical strength to the thermal storage module.

According to embodiments of the present invention, the HS unit isprovided with a plurality of heat conducting elements arranged for beingin contact with the first PCM material. The heat conducting elements maybe further in contact with at least one inner surface of the HS unit. Byproviding heat conducting elements a faster transfer of thermal energycan be realized from the heat transfer fluid in the FT unit to the PCMin the HS unit. In this way, the PCM is charged or discharged faster andmore efficient.

According to embodiments of the present invention, the heat conductingelements may be made from a heat conducting material. For example theheat conducting elements can made of a metal having good thermalconduction properties e.g. aluminium. In this way, the thermal energycan be quickly transferred from the outer surface to the first PCMmaterial and vice versa, thereby allowing for a faster response to atemperature change.

According to embodiments of the present invention, the heat conductingelements are in the form of a porous structure having a predeterminedporosity. The volumetric porosity of this porous structure may bebetween 75% and 98%, preferably between 88% and 95% with respect to thevolume of the porous structure. It has been found that by providing ahighly porous structure the volume taken by this structure otherwiselost to add PCM is limited. For example, the porous structure is made ofmetal foam. Structures like metal foam allow thermal energy to bedistributed more efficiently throughout the first PCM material making itpossible to use the volume of the PCM material more efficiently and thusmake it possible to more efficiently use the HS unit by making more useof the possibility of more efficiently transporting the thermal energyinside the first PCM material and not only of the contact surface of theHS unit. The metal foam has a surface-to-volume ratio (SVR) ranging from300 m²/m³ to 1500 m²/m³ measured using a micro computed tomographyscanning technique. The metal foam has an average cell diameter of 10 mmor smaller measured using a micro computed tomography scanningtechnique.

According to embodiments of the present invention, the thermal storagesystem may be provided with at least two thermal storage modulesconnected to each other via the inlet and outlet ports of theirrespective FT units. Furthermore, a connecting element may be providedfor connecting the input and output points of each thermal storagemodule so as to provide a thermal storage system of a predeterminedshape, e.g. by connecting two thermal storage modules at a 90 degreeorientation a thermal storage system having an L-shape may be provided.It should be understood that other thermal storage configurations arepossible, e.g. by connecting three thermal storage units in a 90 degreeorientation a U-shaped thermal storage system may be provided. In thisway different configurations of the thermal storage system may beprovided, thereby allowing for the thermal storage system to be used ina variety of applications, for instance as walls of a temperaturecontrolled container.

According to preferred embodiments of the present invention, the thermalstorage system is passive. Although the thermal storage system couldalso be active, as opposed to passive. Passive thermal storage systemsare while in use not coupled with an active thermal system and externalpower supply. The external power supply in active thermal storagesystems usually comprise a heat pump, for example employing thewell-known refrigeration-type cycle, while in use moving thermal energyin the opposite direction of spontaneous heat flow and, in order toperform that work, require an external power supply. As such the thermalstorage system can continuously be charged or discharged during use.Passive thermal storage systems on the other hand while in use, i.e. formaintaining a payload space at a predetermined temperature or in apredetermined temperature range, while in use preferably do not requirean external power supply moving thermal energy in the opposite directionof spontaneous heat flow. For example, such thermal storage systems canbe used in the development of passive temperature controlled containerunits used for transporting, usually in a temperature insulated payloadspace, temperature sensitive products that need to be maintained at apredetermined temperature for an extended period of time without theneed of connection to such external power supply. As these passivethermal storage systems cannot be charged while in use, they need to becharged before usage, and therefore require to be connected releasablyto a heat transfer system. In order to optimise the logistics processthis charging needs to be fast and reliable, moreover, the capacity overvolume/mass ratio of the thermal storage system needs to be as high aspossible.

According to embodiments of the present invention, the inlet port and/oroutlet port, which are arranged for being releasably connected to theheat transfer fluid system, are in the form of a male/female connector.Such connectors have been found to allow a relatively easy way ofreleasably connecting the connector to the heat transfer fluid system.

According to a second aspect of the present invention a method isprovided for charging the first PCM material of the at least one thermalstorage system. The method comprises the following steps:

a) providing a heat transfer fluid system, such as a chiller, e.g. aliquid ice production chiller, or a boiler, with or without a reservoirfor the heat transfer fluid;

b) connecting the heat transfer fluid system to the inlet and outletports of the thermal storage system forming a closed circuit for theheat transfer fluid;

c) operating the heat transfer fluid system such that the heat transferfluid is supplied to the at least one FT unit passageway via the inletports of the at least one FT unit;

d) operating the heat transfer fluid system such that the heat transferfluid supplied in step c) is released from the at least one FT unitpassageways via the outlet ports of the at least one FT unit;

e) charging of the first PCM during a certain period of time duringwhich the PCM at least partially changes phase depending on the desiredenergy content;

f) removing the heat transfer fluid from the passageways or keeping theheat transfer fluid at least partially in the passageways of the FTunits of the thermal storage system before, during or afterdisconnecting the thermal storage system from the heat transfer fluidsystem.

According to embodiments of the present invention, the heat transferfluid system comprises a hydraulic circuit arranged for supplying theheat transfer fluid to and releasing the heat transfer fluid from thethermal storage system. For example, the heat transfer fluid system maybe an external system to which the thermal storage system may beconnected, such as a chiller or a boiler. The heat transfer fluid systemmay comprise at least one reservoir for storing the heat transfer fluidpumped in and out of the at least one fluid transportation unit. Thehydraulic circuit may comprise a pump arranged for pumping the heattransfer fluid in an out of the at least one fluid transportation unit.The pump may be configured for pumping the heat transfer fluid at apredetermined speed or flow rate.

According to a third aspect of the present invention a temperaturecontrolled container may be provided, which may be arranged formaintaining a payload space at a predetermined temperature or in apredetermined temperature range. The temperature controlled containermay be provided with a thermally insulated payload space arranged forreceiving temperature sensitive products. Furthermore, a thermal storagesystem according to any one of the embodiments above may be positionedat a predetermined location in the thermally insulated payload space.The temperature controlled container may be mobile. According topreferred embodiments of the present invention, the unit of the FT unitand the HS unit having a temperature which is closest to the ambienttemperature in which the temperature controlled container is kept, isput closest to the outside of the container. It has been found that suchconfiguration limits the heat losses to the ambient environment in whichthe container is kept.

According to yet a third aspect of the present invention a method forproviding a temperature controlled container is provided, the methodcomprising the steps of:

a) providing a container unit having a thermally insulating payloadspace arranged for receiving temperature sensitive products;

b) providing at a predetermined location in the payload space at leastone thermal storage system according embodiments of the first aspect ofthe present invention, the thermal storage system being arranged formaintaining the payload space at a predetermined temperature or in apredetermined temperature range for a predetermined amount of time;

c) releasably connecting the inlet and outlet ports of the thermalstorage system to a heat transfer fluid system, the heat transfer fluidsystem being arranged for forming a closed circuit with the at least oneFT unit of the thermal storage system allowing circulation of the heattransfer fluid;

d) at least partially charging or discharging the first PCM material ofthe at least one thermal storage module according to the method forcharging the thermal storage system;

f) removing the heat transfer fluid from the passageways or keeping atleast partially the heat transfer fluid in the passageways of the FTunits of the thermal storage system before, during or afterdisconnecting the thermal storage system from the heat transfer fluidsystem.

Then the temperature of the payload volume of the temperature controlledcontainer remains within a predetermined temperature range for a certainperiod of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further elucidated by means of the followingdescription and the appended figures.

FIGS. 1 to 3 show three-dimensional views of an FT unit according toembodiments of the present invention.

FIG. 4 shows a cross-sectional view of a first exemplified thermalstorage system according to embodiments of the present invention.

FIGS. 5 to 6 show side views of a second exemplified thermal storagesystem according to embodiments of the present invention.

FIGS. 7 to 8 show exemplified perspective views of a thermal storagesystem with separate FT and HS units according to embodiments of thepresent invention.

FIGS. 9 to 14 show exemplified perspective views of a thermal storagesystem comprising an extruded profile according to embodiments of thepresent invention.

FIGS. 15 to 17 shows exemplified embodiments of a thermal storage systemhaving a stacked configuration.

FIG. 18 show a cross-sectional view of an exemplified thermal storagesystem having an L-shape according to embodiments of the presentinvention

FIGS. 19 to 22 show cross-sectional views of an exemplified temperaturecontrolled container unit according to embodiments of the presentinventions.

MODES FOR CARRYING OUT THE INVENTION

The present invention will be described with respect to particularembodiments and with reference to certain drawings but the invention isnot limited thereto but only by the claims. The drawings described areonly schematic and are non-limiting. In the drawings, the size of someof the elements may be exaggerated and not drawn on scale forillustrative purposes. The dimensions and the relative dimensions do notnecessarily correspond to actual reductions to practice of theinvention.

Furthermore, the terms first, second, third and the like in thedescription and in the claims, are used for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order. The terms are interchangeable under appropriatecircumstances and the embodiments of the invention can operate in othersequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in thedescription and the claims are used for descriptive purposes and notnecessarily for describing relative positions. The terms so used areinterchangeable under appropriate circumstances and the embodiments ofthe invention described herein can operate in other orientations thandescribed or illustrated herein.

The term “comprising”, used in the claims, should not be interpreted asbeing restricted to the means listed thereafter; it does not excludeother elements or steps. It needs to be interpreted as specifying thepresence of the stated features, integers, steps or components asreferred to, but does not preclude the presence or addition of one ormore other features, integers, steps or components, or groups thereof.Thus, the scope of the expression “a device comprising means A and B”should not be limited to devices consisting only of components A and B.It means that with respect to the present invention, the only relevantcomponents of the device are A and B.

The present invention will be elucidated by means of the exampleembodiments shown in FIGS. 1 to 22, which will be described in moredetails below.

FIGS. 1 to 3 show an exemplified Fluid Transportation unit (FT) 10according to embodiments of the present invention. The FT unit 10 isprovided with an inlet port 12 a and an outlet port 12 b which may be inon the same side, as shown in FIG. 1, or on opposing sides, as shown inFIG. 2 or 3. The FT unit 10 is provided with at least one passageway 11for circulating a heat transfer fluid between the inlet port 12 a andthe outlet port 12 b. As shown in FIG. 2, the FT unit 10 may be providedwith a plurality of passageways 11, which may be interconnected so as toallow the heat transfer fluid to be circulated between the inlet port 12a and the outlet port 12 b. Furthermore, the FT unit 10 may be providedwith a plurality of passageways, each connected to a separate inlet port12 a and outlet port 12 b. The heat transfer fluid in the FT unit 10 maybe circulated in the passageways 11 in the direction indicated by thearrows, but other flow direction are possible by providing differentpassageway configurations. The FT unit 10 may be provided with anextruded profile defining at least one passageway via which the heattransfer fluid may be circulated between the inlet and outlet ports 12 aand 12 b.

FIG. 4 shows a cross-sectional view of an exemplified thermal storagesystem 100 according to embodiments of the present invention. Thethermal storage system 100 may be provided with a thermal storage module20, which may comprise at least one FT unit 10 having at least one wall15 with a heat exchange surface. The at least one FT unit 10 may beprovided with at least one passageway arranged for circulating a heattransfer fluid, the flow of which is indicated by the arrows, betweenthe inlet port 12 a and the outlet port 12 b. The inlet port 12 a andoutlet port 12 b of the at least one FT unit 10 may be arranged forbeing releasably connected to a heat transfer fluid system 40, such as achiller or a boiler, which is arranged for supplying or releasing theheat transfer fluid from the at least one FT unit 10 via the inlet andoutlet ports 12 a and 12 b. The heat transfer fluid system 40 maycomprise a docking station allowing a more easy connection of thethermal storage module to the supply of heat transfer fluid. The thermalstorage module 10 may further be provided with at least one Heat Storage(HS) unit 13, which may be filled with a first Phase Change Material(PCM) 14, the first PCM 14 being arranged for exchanging thermal energy,for example as latent heat, while at least partially changing from afirst phase to a second phase. The first PCM 14 of the HS unit 13 may bearranged for being in thermal contact, via the wall 15 provided with aheat exchange surface, with the heat transfer fluid circulating in theat least one FT unit 10 such that thermal energy can be transferredbetween the heat transfer fluid and the first PCM 14. The transferredthermal energy may then be stored in the first PCM 14, for exampleduring the transition of the first PCM 14 between a first phase and asecond phase, e.g. between solid and liquid or gas and liquid and viceversa. As shown in FIG. 4, the FT unit 10 may be provided with a wall 15having a heat exchange surface, which may be in direct contact with thefirst PCM of the HS unit 13. This for example may be achieved byproviding a thermal storage module 20 whereby the FT unit 10 inside theHS unit 13 such that the wall 15 of the FT unit 10 may be provided indirect contact with the first PCM 14.

According to embodiments of the present invention, the thermal storagemodule 20 may be provided in the form of a stacked structure, with theFT unit 10 and HS unit 13 having different dimensions, as shown in FIG.5, or identical dimensions, as shown in FIG. 6. For example, the thermalstorage module 20 may be provided in the form of a stacked structure byproviding the FT unit 10 and HS unit 13 as separate units, as shown inFIG. 7. In this configuration, the separate FT and HS units 10 and 13can be positioned on top of one another such that their respectivethermal contact surfaces may be provided in thermal contact, as shown inFIG. 8. Alternatively, the thermal storage module 20 may be provide dinthe form of a stacked structure by extruding the FT unit 10 and the HSunit 13 as a single profile unit. For example, the extruded profile unitmay be provided with openings defining the FT unit 10 passageways 11, acommon wall shared between the FT unit 10 and the HS unit 13, and anumber of ribs 18 defining a space 19 for positioning the first PCM ofthe HS unit 13, which may be covered by a plate 21, as shown in FIG. 10In this configuration, thermal energy is transferred between the heatexchange surfaces of respectively the FT unit 10 and the HS unit 13 viathe common wall. The extruded profile for the FT unit 10 and HS unit 13may be dimensioned according to the requirements of the thermal storagemodule 20. For example, an extruded profile provided with two spaces 19for positioning the first PCM may be provided, as shown in FIGS. 9 and10. Even larger extruded profiles may be provided having a plurality ofspaces 19 for positioning the first PCM or a material for holding thefirst PCM, and a plurality of passageways 11, as shown in FIGS. 13 and14. The FT unit 10 may be dimensioned such that it is smaller than orsubstantially equal to the HS unit 13 dimensions. Furthermore, it shouldbe understood that the FT unit 10 may be provided with larger dimensionsthan the HS unit 13.

According to embodiments of the present invention, the heat transferfluid may be a pumpable multi phase fluid comprising at least onesubstance which changes phase while circulated through the FT unit 10.The multi phase heat transfer fluid may be a two-phase fluid arrangedfor changing between a solid phase and a liquid phase, which may becirculated between he inlet and outlet ports, which offers theadvantages of higher heat transfer coefficient, thus fastercharge/discharge, and a more constant temperature during heat transferresulting in a better thermal matching between the temperature profilesof the heat transfer fluid and the first PCM 14. For example, themulti-phase heat transfer fluid may be a liquid with solid particleswhich change phase during heat transfer. This can be PCM slurry or anice slurry. Furthermore, a portion of the heat transfer fluid circulatedbetween the inlet an outlet ports 12 a and 12 b may remain in thepassageways 11 upon disconnecting the thermal storage system from theheat transfer fluid system.

According to embodiments of the present invention the HS unit 13 may beprovided in the form of a container having at least one wall with a heatexchange surface, e.g. a closed volume container. The HS unit 13 may befurther provided with a filing port, which is not shown, which can beused for filling or extracting or replenishing or replacing the firstPCM 14 of the HS unit according to the needs of the thermal storagemodule 20.

According to embodiments of the present invention, the thermal storagemodule 20 may be provided in the form of a stacked structure providedwith a number of HS units 13 in thermal contact with at least one FTunit 10. For example, as shown in FIG. 15, the thermal storage module 20may be provided with an FT unit 10 sandwiched between two HS units 13such that their respective walls 15 and 16 are in contact with oneanother, thereby ensuring that thermal energy can be transferred betweentheir respective heat exchange surfaces. As previously described the FTand HS units may be in the form of separate units, similar to the onesin FIG. 7, or in the form of an extruded profile, as explained withreference to FIGS. 9 to 14.

As shown in FIG. 7, the passageways of a rectangular cross-section. Sucha cross-section has been found to provide an improved usage of theavailable space as the usage of the material to make up the passagewayscan be decreased and the volume of the fluid going through thepassageways can be increased, further improving the energy density.

According to embodiments of the present invention, the thermal storagemodule 20 may be provided with a plurality of alternating layers of HSunits 13 and the FT units 10 so as to increase the thermal energystorage. For example, as shown in FIG. 16, the thermal storage module 20may be provided with three HS units 13 and two FT units 10 sandwiched inbetween the HS units 13 such that their respective heat exchangesurfaces are in thermal contact with one another. Furthermore, in thecase where the thermal storage module 20 is in the form of an extrudedprofile, the stacked structure may be realised by positioning aplurality of extruded profiles on top of one another as shown in FIG.17.

According to embodiments of the present invention, the at least one HSunit 13 may be provided on the inside of the closed volume containerwith a plurality of heat conducting elements arranged for being at leastpartially in contact with the first PCM 14. For example, the heatconducting elements, may be made of a metal having predetermined heatconduction properties so that the thermal energy can be more efficientlyexchanged between the heat exchange surface of the HS unit 13 and thefirst PCM 14. For example, the heat conducting elements may be made fromaluminium or another suitable metal with good heat conductingproperties. The heat conducting elements may be in the form of a porousstructure having a predetermine porosity and which is at least partiallysubmerged in the first PCM 14. The porous structure may be in the formof an open cell porous structure, which may have a volumetric porositybetween 75% and 98%, preferably between 88% and 95% with respect to thevolume of the porous structure.8. For example, the porous structure maybe made from metal foam, which may have a surface-to-volume ratio (SVR)ranging from 300 m²/m³-1500 m²/m and an average cell diameter of lessthan 10 mm. For example, the metal foam may be provided in the form ofslabs, which can be fitted in the spaces 19 provided between the ribs 18of the thermal storage module 20 extruded profile.

According to embodiments of the present invention, the HS unit 13 and/orFT unit 10 may be provided with a substantially beam like shape with theheight being significantly smaller than the width and length. Forexample, the HS unit 13 and/or FT unit 10 may be provided in the form ofsubstantially rectangular panels. According to embodiments of thepresent invention the HS unit 13 and/or FT unit 10 may be provided witha height between 1 mm and 40 mm. The height direction 22 along which theheight can be measured is for example shown in FIG. 15. It should beunderstood that the FT unit 10 and the HS unit 13 may be provided withdifferent shapes depending on the requirement of the thermal storagesystem 100. Furthermore, the walls of the HS unit 13 and/or the FT unitmay have a predetermine shape. For example, the HS unit walls 16 and/orthe FT unit walls 15 may have an undulated form.

According to embodiments of the present invention, the thermal storagesystem 100 may be provided with a plurality of thermal storage modules20. For example, the thermal storage system 100 may be provided with afirst and a second thermal storage modules 20 which may be connected toone another via their respective inlet and outlet ports 12 a and 12 b,thereby forming a continuous structure having a predetermined shape, asshown in FIG. 8. A connecting element 17 may be provided for connectingthe inlet and outlet ports 12 a and 12 b of adjacent thermal storagemodules 20, as shown in FIG. 8. According to embodiments of the presentinvention, the connector 17 may be used for connecting a plurality ofthermal storage modules 20 in a variety of shape configuration to matchthe needs of the payload space. For example, the connector 17 may beused to connect the thermal storage units 20 in a 90 degreesorientation, thereby providing a thermal storage system having aU-shape, an L-shape, etc. depending on the number of thermal storagemodules 20 connected to one another. Furthermore, the connector 17 maybe used to connect several thermal storage modules in a substantiallyflat configuration. The connector 17 and the corresponding inlet andoutlet ports 12 a and 12 b can for example be in the form of cooperatingmale/female connectors. The connecting elements 17 can be part of adocking station.

According to embodiments of the present invention, the thermal storagesystem 100 may be used in a variety of applications. For example, thethermal storage system 100 may be used for storing excess “heat” or“cold” energy from a boiler or chiller which can be used at a later timewhen there is a heating or cooling demand. The heat or cold stored inthe thermal storage system can also be used to maintain a payload spaceof a temperature controlled container unit 30, as shown in FIGS. 19 to22, at a predetermined temperature or within a predetermined temperaturerange For example, the thermal storage system 100 may be positioned atan inner wall of a temperature controlled container 30 provided with apayload space arranged for receiving temperature sensitive goods. Forexample, as shown in FIG. 19 the thermal storage system 100 may bepositioned, without any limitation with regards to the positioning ofthe thermal storage unit in the payload space, at a top inner wall ofthe temperature controlled container unit 30. The temperature controlledcontainer unit 30 may be provided with a container unit connector 34,which is in contact with the inlet and outlet ports 12 a and 12 b of thethermal storage system 100. The temperature controlled container unit 30may be provided with an insulated layer 32 for insulating the payloadspace 35. The container unit connector 34 may be arranged for releasablyconnecting the thermal storage unit inlet and outlet ports 12 a and 12 bto a heat transfer fluid system 40. The heat transfer fluid system 40may be arranged for circulating the heat transfer fluid through the atleast one FT unit 10 of the thermal storage system 100 via the at leastone inlet and outlet ports 12 a and 12 b, so as to charge or dischargethe PCM 14 of the at least one HS unit 13, as shown in FIG. 20. In thecase where the thermal storage unit is provided with HS units 13 havingdifferent PCMs, the heat transfer fluid may be circulated until all PCMsare charged/discharged. For example, the heat transfer system may beprovide with a hydraulic system, which may comprise a pump, arranged forpumping and releasing the heat transfer fluid from the thermal storagesystem 100. The heat transfer fluid system 40 may be provided with aconnector 41, which may connected to the container unit connector 34 viapipes 42 and 43. In this way, the heat transfer fluid is circulated inthe thermal storage system 100 so as to charge the first PCM material ofthe thermal storage modules 20. Once the charging process is completedthe heat transfer fluid system 40 is disconnected from the connector 34,and the heat transfer fluid is at least partially maintained in the atleast one passageways of the at least one FT unit 10. According toembodiments of the present invention, the thermal storage system 100 maybe provided in a number of different configurations. For example, asshown in FIG. 21, the thermal storage system 100 may provided in anL-shape so as to cover two of the inner walls of the temperaturecontrolled container. Furthermore, the thermal storage system 100 may beprovided at a suitable shape to cover three walls of the container, suchas U-shape, or all of the walls of the temperature controlled container30, as shown in FIG. 22.

According to embodiments of the present invention, a method for chargingthe first PCM material of the at least one thermal storage system of thepresent invention may be provided. The method may comprise the steps of:

-   -   a) providing a heat transfer fluid system, such as a chiller,        e.g. a liquid ice production chiller, or a boiler, with or        without a reservoir for the heat transfer fluid;

b) connecting the heat transfer fluid system to the inlet and outletports of the thermal storage system forming a closed circuit for theheat transfer fluid;

c) operating the heat transfer fluid system such that the heat transferfluid is supplied to the at least one FT unit passageway via the inletports of the at least one FT unit;

d) operating the heat transfer fluid system such that the heat transferfluid supplied in step c) is released from the at least one FT unitpassageways via the outlet ports of the at least one FT unit;

e) charging of the first PCM during a certain period of time duringwhich the PCM at least partially changes phase depending on the desiredenergy content;

f) removing the heat transfer fluid from the passageways or keeping theheat transfer fluid at least partially in the passageways of the FTunits of the thermal storage system before, during or afterdisconnecting the thermal storage system from the heat transfer fluidsystem.

1. A passive thermal storage system for storing thermal energy in apredetermined temperature range, the thermal storage system comprisingat least one thermal storage module comprising: a fluid transporting(FT) unit comprising: a passageway configured for circulating a heattransfer fluid therethrough; and an inlet port for the inflow of theheat transfer fluid to the passageway and the outlet port for theoutflow of the heat transfer fluid from the passageway, wherein theinlet port and an outlet port of the FT unit are releasably connectableto a heat transfer fluid system, the heat transfer fluid system beingconfigured for circulating the heat transfer fluid through the FT unitof the thermal storage system via the inlet and outlet ports; and afirst Heat Storage (HS) unit at least partially filled with a firstPhase Change Material (PCM), wherein the first HS unit comprises acontainer at least partially filled with the first PCM material; whereinthe thermal storage module is in the form of a stacked structurecomprising the FT unit having a first wall with a first heat exchangesurface, and the first HS unit having a second wall with a second heatexchange surface, the first and second heat exchange surfaces being inthermal contact with each other such that thermal energy can betransferred between the heat transfer fluid in the FT unit and the firstPCM in the first HS unit so that the first PCM of the first HS unit canat least partially change phase in the predetermined temperature range.2. The thermal storage system according to claim 1, wherein the heattransfer fluid is a pumpable single phase fluid.
 3. The thermal storagesystem according to claim 1, wherein the heat transfer fluid is apumpable multi phase fluid.
 4. A passive thermal storage system forstoring thermal energy in a predetermined temperature range, the thermalstorage system comprising a thermal storage module comprising: a fluidtransporting (FT) unit (10) comprising: a passageway configured forcirculating a heat transfer fluid therethrough; and an inlet port forthe inflow of the heat transfer fluid to the passageway and an outletport for the outflow of the heat transfer fluid from the passageway;wherein the inlet port and the outlet port of the FT unit are releasablyconnectable to a heat transfer fluid system, the heat transfer fluidsystem being configured for circulating the heat transfer fluid throughthe FT unit of the thermal storage system via the inlet and outletports; and a Heat Storage (HS) unit at least partially filled with afirst Phase Change Material (PCM); wherein the first PCM of the HS unitis configured for being in thermal contact with the heat transfer fluidof the FT unit such that thermal energy can be transferred between theheat transfer fluid in the FT unit and the first PCM in the HS unit sothat the first PCM of the HS unit can at least partially change phase inthe predetermined temperature range; wherein the heat transfer fluid isa pumpable multi phase fluid comprising a substance which changes phasewhile circulated through the FT unit.
 5. The passive thermal storagesystem according to claim 3, wherein the multi phase heat transfer fluidis a two-phase fluid configured for changing between a solid phase and aliquid phase.
 6. The thermal storage system according to claim 5,wherein the multi phase heat transfer fluid is in the form of an iceslurry.
 7. The thermal storage system according to claim 3, wherein themulti phase heat transfer fluid is a second PCM.
 8. The thermal storagesystem according to claim 7, wherein the second PCM has a phase changingtemperature range different from the predetermined temperature range. 9.The thermal storage system according to claim 1, wherein the heattransfer fluid remains within the FT unit upon disconnecting the thermalstorage system from the heat transfer fluid system.
 10. The thermalstorage system, according to claim 4, wherein the thermal storage moduleis in the form of a stacked structure comprising the FT unit having afirst wall with a first heat exchange surface and the HS unit having asecond wall with a second heat exchange surface, the first and secondheat exchange surfaces being in thermal contact with each other.
 11. Thethermal storage system according to claim 1, wherein the first andsecond walls are substantially the same.
 12. The thermal storage systemaccording to claim 1, wherein the stacked structure comprises a secondHS unit, the first HS unit being in thermal contact with the first wallof the FT unit, the second HS unit being in thermal contact with asecond wall of the FT unit.
 13. The thermal storage system according toclaim 12, wherein the stacked structure comprises a plurality ofalternating layers of the first HS unit and the FT unit being in thermalcontact with each other.
 14. The thermal storage system according toclaim 1, wherein the first HS unit is a closed volume container.
 15. Thethermal storage system according to claim 1, wherein the first HS unitcomprises a plurality of heat conducting elements configured for beingin thermal contact with the first PCM material.
 16. The thermal storagesystem according to claim 15, wherein each of the plurality of heatconducting elements are in the form of a porous structure having apredetermined porosity and are at least partially submerged in the firstPCM.
 17. The thermal storage system according to claim 16, wherein theporous structure is an open cell porous structure.
 18. The thermalstorage system according to claim 16, wherein a volumetric porosity ofthe porous structure is between 75% and 98%.
 19. The thermal storagesystem according to claim 16, wherein the porous structure is a metalfoam.
 20. The thermal storage system according to claim 19, wherein themetal foam has a surface-to-volume ratio (SVR) between 300 m²/m³ and1500 m²/m³.
 21. The thermal storage system according to claim 19,wherein the metal foam has an average cell diameter of less than 10 mm.22. The thermal storage system according to claim 1, wherein at leastone of the first HS unit and the FT unit has a substantially beam likeshape with a height being significantly smaller than a width and alength.
 23. The thermal storage system according to claim 22, wherein atleast one of the first HS unit and the FT units have a height between 1mm and 40 mm.
 24. The thermal storage system according to claim 4,wherein the FT unit comprises an extruded profile comprising thepassageway for the heat transferring fluid.
 25. The thermal storagesystem according to claim 4, wherein the thermal storage modulecomprises an extruded profile comprising the passageway for the heattransferring fluid.
 26. The thermal storage system according to claim 4,wherein the thermal storage system comprises a second FT unit connectedto the first FT unit via the inlet and outlet port ports.
 27. Thethermal storage system according to claim 26, further comprising asecond thermal storage module comprising a second inlet port and asecond outlet port, and a connecting element on the thermal storagemodule configured form at least part of a connection between the inletport and the second inlet port.
 28. The thermal storage system accordingto claim 26, wherein the thermal storage system has an L-shape or aU-shape.
 29. A method for charging the first PCM of the thermal storagesystem according to claim 1, the method comprising the steps of: a)providing a heat transfer fluid system, such as a chiller or a boiler;b) connecting the heat transfer fluid system to the inlet and outletports of the thermal storage system to form a closed circuit for theheat transfer fluid; c) operating the heat transfer fluid system suchthat the heat transfer fluid is supplied to the passageway of the FTunit via the inlet port of the FT unit; d) operating the heat transferfluid system such that the heat transfer fluid supplied in step c) isreleased from the passageways of the FT unit via the outlet port of theFT unit; e) charging of the first PCM for a time period during which thePCM at least partially changes phase; and f) removing at least some ofthe heat transfer fluid from the passageway of the FT unit before,during or after disconnecting the thermal storage system from the heattransfer fluid system.
 30. The method for charging the first PCMaccording to claim 29, wherein the heat transfer fluid system comprisesa hydraulic circuit configured to circulate the heat transfer fluidthrough the FT unit of the thermal storage system.
 31. The method forcharging the first PCM according to claim 30, wherein the hydrauliccircuit comprises a pump.
 32. A temperature controlled container unitcomprising: a thermally insulated payload space arranged for receivingtemperature sensitive products; and at least one thermal storage systemaccording to claim 1, positioned in the thermally insulated payloadspace.
 33. The temperature controlled container unit according to claim32, wherein the temperature controlled container unit is mobile.